Reversible Phase Transformation in Polycrystalline TRIP Steels Induced by Cyclic Indentation Performed at the Nanometric Length Scale

Abstract

Metastable austenitic stainless steels are an interesting group of materials, which exhibit the Transformation Induced Plasticity effect. In this regard, phase transformation from austenite to martensite enhances the work hardening of the metastable austenitic stainless steels affecting the deformation dynamics and mechanical properties including fatigue properties. Within this context, the reversible load‐induced phase transformation from γ to ϵ ‐martensite is investigated at the local scale under cyclic indentation. This reversible phase transformation is manifested itself by a combination of hysteresis loops, elbow formation, and reversible pop‐ins in the loading curve. The initial cyclic achieved through the nanoindentation technique allows to identify three different deformation regimes for the <111> austenitic grains. Firstly, a softening effect takes place due to the dislocation activation; subsequently the phase transformation induces a hardening effect and finally, the load deformation curve reaches a plateau where no more plastic deformation is observed.